TW469707B - Method and device for echo cancelling - Google Patents

Abstract

Echo cancelling in a communication line system, particularly an ISDN or XDSL system, is performed by means of a tunable hybrid (5) which comprises tunable passive elements and is integrated in the analog part of the front end (3), whereby the values of the tunable passive elements are controlled by digital control means (4), for example a microprocessor.

Description

46970 7 A7 B7 V. Description of the invention ο) (Please read 11 · Notes on the back before filling this page) The present invention is a method for canceling the reply in the communication line system, especially in the integrated service digital network (abbreviation Is ISD N) or any digital subscriber line (abbreviated as XDL S). Echo cancellation is generally handled at the analog front end of the communication line system, especially between linear transformers, digital to analog, and analog to digital converters. The analog front end is the part of the two-wire connection and the interface of the digital transmitting and receiving device connected to the two-wire connection. It is well known that echo cancellation can be realized by a digital filter technology. Another well-known method is the synthesis of a digital mixed impedance on the digital side of the A / D converter. US — A-5. 28 7 The aforementioned method is described in US Patent 406. A digital balance circuit that operates as a cancellation return echo to a two-wire / four-wire conversion mechanism. These digital methods, which are used to eliminate the echo, cannot sufficiently remove the original nonlinear distortion phenomenon on the analog front end on the RX and TX paths. The present invention seeks to propose a method which avoids the aforementioned disadvantages. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs. According to the present invention, the response retrieval is implemented through a hybrid including an adjustable passive element, thereby enabling the adjustable passive element to be controlled by a digital control mechanism. Control and adjustment. Tuning is analog, but control is digital. Since the adjustable echo cancellation is achieved before any digital processing, this method is different from the digital echo cancellation method. It improves the noise ratio of reception and transmission, and can also correct the non-linear distortion phenomenon of the aforementioned analog front end. The aforementioned nouns ~ include 〃 here in a non-limiting meaning. This paper size is applicable to the Chinese National Standard (CNS) A4 (210 X 297 mm). The clothing printed by the staff consumer cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs is applicable to the Chinese standard (CNS) A4 (2) 0 X 297 mm. ) A7 B7__ 5. Description of the invention (2) Preferably, the above-mentioned variable passive element uses a scale factor 'for example, it is allowed to be implemented in an integrated circuit. The adjustment method of such a passive element includes the evaluation of the τχ return distortion 値 in the hybrid component, so that when the gain is not equal to zero, the digital control mechanism adjusts the adjustable to the adjustable passive element until the zero is obtained. Gain. The device of the present invention, and the method particularly suitable for carrying out the above method, include a hybrid component, which is an analog front end integrated in a communication line system, and includes an adjustable passive element that can control its cymbal. -—A digital control mechanism * This digital control mechanism is connected to the hybrid component as a control of the variable passive components. The passive component can be connected to the chip, thereby effectively utilizing the cost-effectiveness of the device. The hybrid component may include a hybrid bridge circuit and a current-to-voltage converter. The hybrid bridge circuit includes two identical branches, each of which contains two impedances in series: one of which is an adjustable balanced impedance. The digital control device may include a microprocessor. ~ This invention will be described by way of examples and drawings, in which FIG. 1 shows an interface block diagram of a line in a communication line system and a terminal portion of a transmitting and receiving device; FIG. 2 shows the interface of FIG. 1 in an overview "Echo Cancellation Device" Fig. 3 depicts the echo cancellation device shown in Fig. 2 in detail. ^----— — — — — — I!. I I Ϊ Order! —! 1 (Please read the precautions on the back before filling this page) 469707 V. Description of the invention (3) Comparison table of main components A7 B7 1 2345678 9

2 A 4 Printed by the Intellectual Property Bureau of the Ministry of Economic Affairs, Consumer Cooperatives 78 Circuit line transformer front-end components Digital control device Hybrid component Digital / analog converter Attenuator driver Programmable amplifier amplifier analog / digital converter Line end resistance Line end resistance Hybrid bridge circuit current and voltage converter transmission path transmission path reception path reception path branch amplifier digital transmission and reception device (please read the precautions on the back before filling this page)-I ----- 丨 丨 Order * --- -I --- The paper size ig uses the Chinese National Standard (CNS) A4 specification (210x 297 public field) -ό-Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs 6 970 7 A7 __B7__ V. Description of the Invention (4) Figure 1 depicts an interface that is located between one end of a two-wire line with an integrated service digital network or impedance XD SL network, and the other end is, for example, a digital transmitter and receiver from a modem. The ends T and R of the device 21. This interface basically includes a line converter 2 with a transformer ratio of 1 to η, and one of the four connection pins TX0, TX1, RX0, and RX1 connected to the front end 3. The front end 3 is connected to the digital transmitting and receiving device 2. The end portions T and R of 1 are integrated with an echo cancellation device. The echo cancellation device includes a splitter 5 and a digital control mechanism 4 (such as a microprocessor). ^ A digital / analog converter 6, a filter 7 and a driver 8 are installed before the splitter 5 in the transmitting or transmitting direction (TX direction). In the receiving or RX direction, a programmable gain amplifier 9 (to ensure a fixed output power, a filter 10, and an analog-to-digital converter 1 1) is connected after the splitter 5 »In the direction of TX, TX0 and TX 1 is connected to converter 2 via line-end resistor 1 2. This resistor 12 is a protection resistor to limit power dissipation to the splitter and analog front end, and has ~ impedance 値 is Rt / 2n2, where η is the aforementioned converter 2 Conversion ratio. Typical 1 ^ 1 resistor 値 is 50 ohms. Pins RX 0 and RX 1 are connected to converter 2 via a line end register 1 2 A having the same resistance 値 as above. In Figure 2 Here, the splicer 5 that can be made into an integrated circuit is composed of a differential bridge circuit 13 and a current-to-voltage converter 14. This paper scale uses the Chinese National Standard (CNS) A4 觇Grid (210 x 297 male "Π ------------- install -------- order --------- line ,. C please read the first Note the $ item and fill in this page again.) A7 469707 ___B7__ V. Description of the invention (5) The differential bridge 13 starts from the output terminals of the driver 8 1 5A and 16A TX paths 1 5 and 16 and finally At the input terminals 17A and 18A of the programmable gain amplifier 1, the RX paths 17 and 18 are respectively connected to these ends 15A, 16A, 17A and 18A to the connection pins TXO, TX1, RX1 and RX0. I, the difference The dynamic bridge 1 3 contains two identical branch circuits 1 9 1 These branches are connected to the terminals ϊ 5A and 1 6A at the output side of the driver 8 by connecting pins RX and RX1. Each branch circuit 1 Both 9 include two series impedances: balanced impedance Z »and impedance Z2. The impedance Z2 of one of the branch circuits 19 is connected in series between the terminal 15A and the balanced impedance Zb, and the other end of this balanced impedance is Connect to the connection pin RX 0. The impedance 22 on the other branch 19 is connected in series between the terminal 16 A and the balanced impedance Z b. The other end of the balanced impedance Z b is connected to the connection pin. Pin RX1. ≫ Impedance Z 2 and impedance Z b include adjustable passive components, such as resistors, capacitors and inductors. These components are controlled by the microprocessor 4. How to adjust these components will be discussed in the next section. And, the factor k is used as one of the passive elements of impedance Z 2 and Z b. These impedances can be placed in a single chip, for example. The scale factor can be, for example, 100 or 100. As shown in the detailed diagram of FIG. 3, each balanced impedance Zb includes an adjustable resistor Rci An adjustable resistor 111 is connected in parallel with the adjustable capacitor C i in series. Finally, the adjustable resistor 111 is connected to a non-required adjustable standard. The paper size applies the Chinese National Standard (CNS) A4 specification (210 x 297 Gong) (Please read the notes on the back before filling out this page) I 丨 丨 I ί I order. — — Jill — ·. Printed by the Intellectual Property Bureau Staff Consumer Cooperatives of the Ministry of Economy 469707 A7 B7 V. Description of the invention ( 6) Resistor R3, 値 of this resistor R3 is 2 kRt / 2 η2 * where k is the proportionality factor, and 値 2 kRt / 2 η2 has been described corresponding to the aforementioned planes of the terminal resistances 12 and 12A. In the embodiment, the adjustable resistors Ro and RiW and the adjustable capacitor C include a plurality of discrete small series resistors and small parallel capacitors, respectively. The trimming is through the control register of the microprocessor 4 with or without a small resistor or capacitor to allow discrete control of the register or capacitor. ^ Another impedance redundancy 2 in each branch circuit includes a non-required resistor R2, including a variable resistor r2 with the same resistance as the resistor r3, which can be scaled to 2kRt / 2n2, and is connected in series with the adjustable capacitor C2 . Inductance of the adjustable capacitor compensation converter 2 In an embodiment, the adjustable capacitor (: 2 includes a plurality of small discrete capacitors connected in parallel, and the microprocessor 4 is connected to the control register or not connected to the control register). The small capacitance is allowed to allow discrete control or fine adjustment of the capacitance. The current-to-voltage converter 14 includes an operational amplifier 20 and two adjustable feedback impedances Z ib, which are the same as the impedance zb. The configuration is therefore a passive component. In order to make the gain impedance of the splitter independent of the setting or frequency, the feedback impedance Zib of the current-to-voltage converter 14 is also adjusted to be the same as Zb, because in this case The current-to-voltage converter 14 can be used as a differential amplifier with gain.-The gain of the voltage Vhyb at the output of the current-to-voltage converter 14 (that is, for the voltage between the pins RXO and RX1) The gain) can be written as: This paper size is applicable to the Chinese National Standard (CNS) A4 specification (2) 0 X 297 male 5n (Jing first read the precautions on the back before filling this page) • 丨 I 丨 — 丨 丨 —Order-- ------ Ministry of Economic Affairs Hui Property Office employees consumer cooperatives printed - 469707 A7 B7 V. invention is described in (7)

Grx = Vhyb / VrX, which is equivalent

Grx = — Zfb / Zb, where 値 is 1, if Zib = Zb. {Please read the notes on the back before filling this page.) Differential bridges 1 and 3 operate in two directions of transmission and reception. In the direction of transmission or TX, the differential bridge 13 receives a voltage signal V tx from the TX driver between the ends 15A and 16A of the paths 15 and 16 and then directly transmits it to the pin τχ 〇 And TX 1 〇 In the direction of receiving or RX, the voltage signal transmitted from wiring 1 is first converted by converter 2 to the voltage between pins RXO and RX1, as shown in Figure 1. f Via the impedance Zb, the obtained current is converted into a voltage Vhyb in the current-to-voltage converter 14. The Programmable Gain Amplifier (PGA) 9 thus compensates the gain of the previous path ’to obtain a total gain, which is the gain from Vtx to Vhyb, and is reduced to one. Vtr is an equivalent wiring voltage source 21 in series with the equivalent impedance of line 1 (as shown by the dashed lines in Figs. 2 and 3), and Vhyb is the output voltage of the current-to-voltage converter 14 " Printed by Employee Consumer Cooperatives. For those who are familiar with this skill, the total gain can be calculated as

GtnirVbyli / Vtrx, Gen [], G.rx = Zfb * (Rt / 2n2) / [Zb (Rl / 2n2) + R, / 2n2 + Zb] * Z.r + ii / 2]

Gtn = Zfb / Zb * (RJ2n2) / (Ri / 2n2 + Zw.ii / 2) -1Ό-This paper size is applicable to China Garden Standard (CNS) A4 gauge pile (210x297 cm) d 6 970 7 A7 B7 Members of the Intellectual Property Bureau of the Ministry of Economic Affairs and Consumer Cooperation have made the selection process so that the selection process will be as follows: V. Invention Description (8) This gain G t will not be affected by the cancellation of the reply. Because the differential bridge 13 is actually a differential impedance bridge, those skilled in the art should know that the best return loss is obtained when the bridge is in equilibrium. When the bridge system is in a balanced state, the TX signal return loss (hereinafter referred to as G t r X; 1) is equal to zero. Therefore, during the initialization period of the system, the TX signal loss gain will be estimated later. Experts who are familiar with this technique can easily derive the TX gain loss gain Gtrxl2 estimate (that is, the self-contained gain, where Vtx is the voltage applied to terminals 15A and 16A), as follows: Lost gain gain:

V

Gtrt = V hyb / V 1 ι

Gtrx = Zfb / Zi * [Zi-Zb-(Ri / 2n2) * (Zir + i! + 2Zb / Zir + ii) divided by [Z2 * ((R, / 2n2) * (Zu + ii + 2Z〇 / Zr + M + Zb)] When the following conditions are met, the loss gain of the TX signal is equal to 0: Z b must be equal to kZ.rtn * (Z2-R1 / 2n1) / (kZtr.1i + 2kRl / 2n2) where k is the scaling factor. This paper scale applies the Chinese National Standard (CNS) A4 grid (210 X 297) "1 (Please read the precautions on the back before filling this page) --- I! I Order ---- --- 1 1 ^. 4 6 970 Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs * 1 A7 B7 V. Description of the invention (9) Z2-Rt / 2 n2 = k 2Rt / 2n2 That is, Z2 = (2k + l ) Κ * / 2η2, and 2 ^ is reduced to Zb = [l / kZu + ii + l / kURVZn2)] _ 1 t. The balanced impedance Z b should be as close as possible to the scale end resistance in parallel with the base line The combination of 値 2 k Rt / 2 η2 and the converter impedance 値 k Z tr + li 値, as mentioned before, the splitter is therefore in equilibrium and can output the best return loss. In the actual situation The TX return loss gain Gtxrl of the splitter is determined by the microprocessor 4 by the digitization of the measured voltage hy V hyb and digitization. Calculated by the known 値 V t *. If the loss gain Gtrxl of the TX signal return of the splitter is not 0, the microprocessor fine-tunes the adjustable passive element in the splitter 5 and goes through the adjustment loop until the 値 is equal to Up to 0. After the adjustment work is completed, the adjustable passive components Ri, (: 1 and (: 2 are the best.) V. An appropriate algorithm is used for this adaptation circuit, such as the well-known $ most滑 滑落 # algorithm. With this algorithm, the microprocessor 4 can change the continuity of different adjustable passive components by positive or negative decrement. Then check its effect on the voltage Vhyb afterwards and finally change The component that causes Vhyb / Vtx to decrease. Such steps will be repeated until the voltage ratio Vhyb / Vtxf is changed again. This voltage is the TX signal loss gain G pri. In one embodiment, especially for XDSL · The application of 'resistance R. Can be between 2 8 and 8 9 6 ohms' voltage Ri can be used in 1 5 and too large paper size due to the network macro standard < T: RS) A4 phase solder X charge 7 km) I!! I I --— nil * I II — 11 — ^ ---— — — — — — I (I must read the precautions for reading δ before filling out this page) 4 6 9 7 Ο T ~ ____ Β7 ____ V. Description of the invention (10) Between 240 ohms and voltage ":: now, 5 and Capacitor C 2 is adjusted between 120 pF and 240 pF. Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs n 1-— nunfn I nt— I n I nn 11 I < Please read the notes on the back before filling out this page) This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

Claims (1)

d 97 0 Τ Β8 _§__ VI. Application for patent scope 1. A method for canceling the echo in a communication line system, wherein the implementation of this method is by adjusting the form of the analog front end of the communication line system. Passive element, so that the adjustable passive element can be controlled by the digital control mechanism (4). 2. The method according to item 1 of the scope of patent application, wherein the scale factor (k) is used to adjust the above-mentioned adjustable passive element. 3. The method according to item 1 of the scope of patent application, wherein adjusting the adjustable passive component includes the step of measuring the TX signal loss gain in the splitter (5), whereby when this gain is not At 0 o'clock, the digital control mechanism (4) passes the adjustment loop to the adjustable passive component until the TX signal return loss gain is obtained. 4. The method according to item 2 or item 3 of the patent application scope, wherein the splitter (5) comprises a differential bridge (13) having two branches (1 9), and each bridge contains two A series of adjustable passive impedances (Z2 and Zb), one of which is an adjustable balanced impedance (Zb), so that the system of the adjustable balanced impedance (Zb) is as close as possible to the line end in the Tx path The scale impedance 値 of the series circuit of the resistance (2Rt / 2 η2), and the line impedance (Z tr i). 5. The method according to item 4 of the scope of patent application, wherein the splitter includes a current-to-voltage converter (1.4), and the adjusted feedback impedance (Zib) is made equal to the adjustable balanced impedance (Zb). 6. —An echo cancellation device in a communication line system 'wherein the device includes:-a splitter (5), which is the analog front end of the communication line system. The paper size of this paper applies the Chinese National Standard (CNS) A4 specification ( 210 x 297 public meals).] 4-丨 11! 111 — -II II! II order * 1 — — — · — —-(Please read the notes on the back of the page before filling out this page) Staff of the Intellectual Property Bureau of the Ministry of Economic Affairs Consumption cooperative printed ¥ clothing d6 970 7 B8 C8 D8 6. The scope of patent application, the splitter (5) contains several adjustable passive components, which can be controlled by the following digital control agencies; a digital control agency (4) , Connected to the splitter (5) 'and included in the device. 7. The device according to item 6 of the scope of patent application, wherein the adjustable passive element of the splitter (5) is scaled by a preset scale factor (k). 8. The device according to item 6 of the patent application, wherein the splitter (5) comprises a differential bridge (13) and a current-to-voltage converter (14). 9. The device according to item 8 of the scope of patent application, wherein the differential bridge circuit (13) includes two identical branch circuits (19), each branch circuit including one in series with a second adjustable impedance (Z2) One is adjustable balance impedance (Z b). 10. The device according to item 9 of the scope of patent application, wherein the adjustable balance impedance (Zb) includes an adjustable resistor (R.), which is connected in parallel with an adjustable circuit (Ri) and an adjustable capacitor (Ci), So in parallel with another resistor (R 3). 1 1. The device according to item 10 of the scope of patent application, wherein the other resistor (R 3) has the same resistance 与 as the line resistance (1 2) located on the TX path, and the proportionality factor (k) is Scaling. 12. The device according to item 9 of the scope of patent application, wherein the second adjustable impedance (22) of each branch circuit (19) includes a resistor (R2) connected in series with an adjustable capacitor (C2), The paper size of this resistor (R2) is applicable to the Chinese National Standard (CNS) Al specification (210 X 297 mm) H ί I nn 1 >. ^ 1 tt 1 bite, · Mae I ir tt I n < Read the notes on the back and fill in this page) Consumption cooperation by employees of the Intellectual Property Bureau of the Ministry of Economic Affairs 钍 15- 469707 D8 VI. Patent application scope 値 (2 kRt / 2 η2) is equal to the line bribe in the TX path The resistance 値 of the resistor (1 2) is the same, and it is scaled by the proportionality factor (k) "1 3. As for the device in the scope of patent application item 9, wherein the current-to-voltage converter (1 4) includes a The adjustable balanced impedance (Z.) has the same impedance and an adjustable feedback impedance (Zfb) operational amplifier (20). 14. The device according to item 6 of the patent application, wherein the digital control mechanism includes a microprocessor (4). 15. The device according to item 6 of the scope of patent application, wherein the adjustable passive component is part of an integrated circuit. ------------ * Install ------- Order -----! Line (Please read the notice on the back before filling out this page) Staff Consumption of Intellectual Property Bureau of the Ministry of Economic Affairs The paper size printed by the cooperative is applicable to the Chinese National Standard (CNS) A4 (210 * 297 mm). · | Ό_